18,524 research outputs found
A Hybrid Adaptive Low-Mach-Number/Compressible Method: Euler Equations
Flows in which the primary features of interest do not rely on high-frequency
acoustic effects, but in which long-wavelength acoustics play a nontrivial
role, present a computational challenge. Integrating the entire domain with
low-Mach-number methods would remove all acoustic wave propagation, while
integrating the entire domain with the fully compressible equations can in some
cases be prohibitively expensive due to the CFL time step constraint. For
example, simulation of thermoacoustic instabilities might require fine
resolution of the fluid/chemistry interaction but not require fine resolution
of acoustic effects, yet one does not want to neglect the long-wavelength wave
propagation and its interaction with the larger domain. The present paper
introduces a new multi-level hybrid algorithm to address these types of
phenomena. In this new approach, the fully compressible Euler equations are
solved on the entire domain, potentially with local refinement, while their
low-Mach-number counterparts are solved on subregions of the domain with higher
spatial resolution. The finest of the compressible levels communicates
inhomogeneous divergence constraints to the coarsest of the low-Mach-number
levels, allowing the low-Mach-number levels to retain the long-wavelength
acoustics. The performance of the hybrid method is shown for a series of test
cases, including results from a simulation of the aeroacoustic propagation
generated from a Kelvin-Helmholtz instability in low-Mach-number mixing layers.
It is demonstrated that compared to a purely compressible approach, the hybrid
method allows time-steps two orders of magnitude larger at the finest level,
leading to an overall reduction of the computational time by a factor of 8
Study of the effect of pH, salinity and DOC on fluorescence of synthetic mixtures of freshwater and marine salts
In order to provide support for the discussion of the fate of organic matter in estuaries, a laboratory simulation was
performed by changing freshwater ionic strength, pH and organic matter content. The change in spectroscopic
characteristics caused by variations in salinity, pH and organic matter concentration in the filtered samples was
observed by UV-Vis and fluorescence spectroscopy. The increase in emission fluorescence intensity of dissolved
organic matter (DOM) due to increasing salinity (in the range 0 to 5 g l−1) is affected by the pH of the samples. The
emission fluorescence intensity at the three maxima observed in the fluorescence spectra, is linearly correlated with
dissolved organic carbon (DOC) concentration at several salinity values in the same sample. The increase in organic
matter concentration caused a shift in the emission peak wavelength at 410 nm for several salinity values.We
concluded that it is necessary to take into account the influence of salinity and pH on emission fluorescence of
dissolved organic matter if it is to be used as a tracer in estuarine or near shore areas
A Method to Tackle First Order Differential Equations with Liouvillian Functions in the Solution - II
We present a semi-decision procedure to tackle first order differential
equations, with Liouvillian functions in the solution (LFOODEs). As in the case
of the Prelle-Singer procedure, this method is based on the knowledge of the
integrating factor structure.Comment: 11 pages, late
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